It is now well known that for some period of time the use of catalytic converters had been proposed for converting the undesirable compounds in automobile and truck engine exhaust gases to provide less objectionable products of combustion and that the converters are now in usage on the majority of new cars presently being produced and sold. The catalytic conversion being effected is primarily one of completing the oxidation of the products of combustion leaving the engine cylinders, i.e., carbon monoxide and unburned hydrocarbons are being further oxidized to harmless carbon dioxide and water vapor. However, in view of the fact that there are some sulfur compounds still present in gasoline for autos, as well as in diesel fuels for both autos and trucks, there has been the conversion of sulfur compounds in the fuel within the engine to form SO.sub.2 and then the catalytic conversion of the SO.sub.2 in the converter to SO.sub.3 and to sulfuric acid (H.sub.2 SO.sub.4). This resultant production of sulfuric acid from the cars with the catalytic converters has now caused considerable concern to the car using public to government officials, to the automobile manufacturers and to the oil refining industry. There is apparently no simple solution to the problem, particularly, where the removal of all of the sulfur from gasoline appears to be a prohibitive procedure by necessitating vast, expensive additions to most all present gaasoline refining facilities. There would also be an additional cost to the resulting gasoline as well as some loss in yield.
In lieu of eliminating or reducing the amount of sulfur present in the grades of gasoline now in use, it is an object of the present invention to provide a catalytic converter system and method of operation where the SO.sub.2 in the engine exhaust stream will be, in effect, by-passed around the catalyst section of the converter and it can be discharged without being converted to SO.sub.3 or H.sub.2 SO.sub.4.
A further object of the invention is to provide a SO.sub.2 adsorbing material in a gas previous bed to essentially remove the SO.sub.2 content of the exhaust stream so that it can be catalytically converted without forming SO.sub.3 or H.sub.2 SO.sub.4 and, in addition, to provide for a rotatable, or otherwise movable, bed of the sorptive material so that the portion(s) thereof picking up SO.sub.2 can be rotated to a desorption zone where the catalytically treated gas stream can effect the removal of the SO.sub.2 from the material and permit its reuse in the system.
As a still further object of the invention, there is the utilization of the exhaust gas stream flow to impinge upon suitably placed vanes or turbine type blades and effect the desired and required movement of the sorptive bed such that no extraneous motive power will be required to operate the novel converter system.
In one embodiment, the present invention is directed to a method for effecting the continuous cataytic conversion of an engine exhaust gas stream and for preventing sulfuric acid formation in the treated gas stream by providing for the continuous by-passing of the SO.sub.2 content of the untreated stream around the catalyst conversion zone, which method comprises the steps of: (a) initially passing the engine exhaust through a SO.sub.2 adsorption zone and into contact with a segmental portion of a gas previous moving bed of SO.sub.2 adsorptive material; (b) passng a resulting substantially SO.sub.2 -free stream from the latter to an adjacent fixed position catalyst zone and into contact with the surface of a conversion catalyst retained therein; (c) passing the resulting catalytic treated gaseous stream at an increased temperature level from the catalyst zone to a desorption zone and therein effecting the contact of a segmental portion of said moving bed of SO.sub.2 adsorptive material to effect SO.sub.2 removal therefrom and the discharge of the combined gaseous stream from the conversion zone; and (d) using the energy of the gas stream flow through at least one of the contacting zones to effect the movement of the SO.sub.2 adsorptive material so that all of the sections thereof will sequentially rotate through the adsorption and desorption zones.
In another embodiment, the invention provides a catalytic converter for engine exhaust gases which provides for by-passing sulfur dioxide around the catalyst section to preclude sulfuric acid in the treated exhaust stream and which comprises in combination, (a) a confined housing with exhaust gas inlet means thereto and a treated gas outlet therefrom; (b) a gas permeable catalyst retaining section with oxidation catalyst therein fixedly positioned within said housing; (c) an additional gas permeable section that retains a SO.sub.2 adsorbent material therein that is rotatably supported within said housing to be maintained adjacent said catalyst section in a manner to permit gas flow between said sections and to provide for the movement of said adsorbent material between an upstream adsorption zone and a downstream desorption zone; (d) gas flow diverter means positioned in said converter to direct the incoming stream through a portion of the SO.sub.2 adsorption section and through a portion of said SO.sub.2 adsorbent material therein so as to pass a substantially SO.sub.1 -free stream to said catalyst section and, additionally, to direct a treated stream from the latter section through said downstream desorption zone to remove SO.sub.2 from the adosrobent material and from the converter, and (e) vane means connective with said rotatable section which are positioned within the exhaust gas stream flow path through the housing whereby the adsorbent material in said rotatable section will be continuously moved therewith between the SO.sub.2 adsorption and desorption zones in the housing.
In the SO.sub.2 adsorption zone, it is of advantage to utilize subdivided particles which can provide a gas pervious bed of the sorptive material and permit the exhaust gas stream to readily pass therethrough and carry on into the catalyst zone for the subsequent catalytic oxidation of the undesired components in the stream. The sulfur components of the gasoline, or other engine fuel, will primarily be converted to sulfur dioxide in the engine; however, some SO.sub.3 or other sulfur compounds may be present and the terminology "SO.sub.2 adsorptive material", as utilized herein, should not be considered limiting since it is preferable that the material will have the capability of adsorbing SO.sub.2 and other sulfur compounds that may be present. For example, the material may comprise alumina, activatd carbon, zeolitic molecular sieve material, etc., which types of material are capable of withstanding relatively high temperature conditions and can adsorb a major proportion of the sulfur compounds present in the exhaust gas stream. The temperature of the exhaust gas stream reaching the converter system can vary depending upon the type of automobile engine involved and the proximity of the converter to the engine itself. Thus, the temperature of the stream may vary from 500.degree. to 1000.degree. F. as it reaches the adsorption material and the inlet face of the catalyst section. On the other hand, the exhaust gas stream, after contact with the catalyst bed, will generally be to an elevated temperature which may be of the order of 200.degree. to 500.degree. F. higher than the inlet temperature to the catalyst zone. Aa a result, the elevated temperature stream can be quite effective in desorbing the SO.sub.2 from the sorptive material in accordance with the operational procedure of the invention. Also, in accordance with the present invention, the sorptive bed will be continuously rotated, or otherwise moved, such that each portion of the bed will move from a sorption zone to a desorption zone and back to the former, whereby a portion of the bed is continuously serving to effect the adsorption of SO.sub. 2 from the gas stream while at the same time a previously contacted portion of the bed is undergoing contact with the treated exhaust gas stream so as to be desorbed and ready for use when it again reaches the sorption zone.
It is also within the scope of the present invention to make use of the velocity of the exhaust gas stream to effect the movement of the bed of sorptive material such that it will be contiuously rotated and moved between a sorption area and a desorption area. For example, the use of a plurlity of radially and angularly positioned blades or vanes in combination with the movable bed of sorptive material and a channeling of the path of the exhaust gas stream flow in a manner to exert resultng force vectors and a rotational effect on the material retaining section, can provide for the desired movement of the sorptive material from one zone to another. It is also within the scope of the invention to utilize a suitable impeller wheel, or a small turbine type wheel, which is placed in the path of the exhaust gas stream and which will drive suitable gearing in turn connective with a shaft that is connected to the center of the retainer for the sorptive material so as to effect the desired rotation of the bed of SO.sub.2 adsorptive material in the system.
Actually, it is not intended to limit the present invention to any one apparatus arrangement for positioning the catalyst in the converter, nor for effecting the placement of a SO.sub.2 adsorptive material in combination therewith, as long as a portion of the sorptive material can provide an initial contact with the incoming exhaust gas stream to remove the SO.sub.2 therefrom and then move to a downstream position with respect to the catalyst such that, at the same time, another portion of the adsorptive material will be extending across the path of the treated gas stream leaving the catalyst to provide for desorption of SO.sub.2 from the bed. In one embodiment, there may be a cylindrical or annular-form SO.sub.2 adsorptive bed which can be rotated around a central cylindrical core of catalytic material such that the incoming exhaust gas stream will first pass through a segmental portion of the SO.sub.2 adsorptive bed prior to contacting the catalyst zone. The incoming gas stream will also contact suitable positioned vanes or turbine type blades associated with the retaining section for the adsorptive bed so that it will be subjected to rotation as long as there is exhaust gas flow.
In another type of apparatus arrangement, the SO.sub.2 sorptive material can be retained within a generally flat disc-like retaining section which is superposed above or along side of a circular-form catalyst section such that the incoming gas stream will pass through a segmental portion of the SO.sub.2 adsorptive material and pass on through an opposing portion of the catalyst section. At the same time, in a generally diametrically opposing portion of the converter, the exhaust gas stream leaving the catalyst section can pass through an opposing segmental portion of the SO.sub.2 sorptive material so as to effect a desorption of SO.sub.2 from the bed. Again, there may be radial vanes or impingement blade means provided in combination with the retaining section for the SO.sub.2 sorptive material such that the incoming exhaust gas stream can effect a continuous rotational movement for such section, an thereby continuously rotate the sorptive material in a manner to have all the portions move between the adsorption area to the desorption area and then back to the adsorption area.
The catalyst section of the converter unit will also be of a type that is gas pervious such that there may be the continuous passage of an exhaust gas stream through the catalyst section to effect contact with the surface of the catalyst material and provide for the catalytic oxidation of the undesired components of the gas stream. It is, of course, not intended to limit the present invention to the use of any one type of catalyst in the converter and typically the catalyst will comprise a coating on a suitable refractory support material which may be in small spherical or pellet form of the order of 1/16 inch to about 1/4 inch or, alteratively, the support may comprise a rigid skeletal honeycomb type of material having a multiplicity of small tubular form passageways therethrough so as to provide a relatively high surface area per unit of volume. Where subdivided particles are used in the catalyst section, the support can be a suitable refractory inorganic oxide such as alumina, silica, silica-alumina, alumina-magnesia, etc., although other inorganic oxide materials may be present as additives such as boria, thoria, calcium oxide, etc. The catalytic coatings may include metals of Groups IIA, IB, VB, VIB, VIIB and VIII, and in particular, copper vanadium, chromium, iron, cobalt, nickel, platinum, palladium, etc., with the components being used singly or in combination with one or more of another active component.
The rigid skeletal "honeycomb" materials may comprise alpha-alumina, alumina-silica-magnesia, zirconia-silica, zircon-mullite, sillimanite, petalite, spodumene, cordierite, alumina-silica, etc. The coatings on the honeycomb type materials may, of course, be similar to the active types of coatings hereto described in connection with the spherical or pelletized types of support materials.